Sperm Gene Is 600 Million Years Old

(Ivanhoe Newswire) --- Just as fashion changes from year to year and culture to culture, so do "sexy" genes, or genes specific to sex – with one critical exception. There is one sex-specific gene  whose function has remained unaltered throughout evolution. That gene, called Boule, is responsible for the production of sperm.

Scientists from the Northwestern University Feinberg School of Medicine discovered that Boule appears to be the only gene known to be exclusively required for sperm production in every organism on earth, from an insect to a mammal.

The discovery of Boule's key role in perpetuating animal species offers insight into male infertility, a potential target for a male contraceptive drug, and a new direction for future development of pesticides or medicine against infectious parasites or carriers of germs.

"This is the first clear evidence that suggests our ability to produce sperm is very ancient, probably originating at the dawn of animal evolution 600 million years ago," senior author Eugene Xu, assistant professor of obstetrics and gynecology at Feinberg, was quoted as saying. "This finding suggests that all animal sperm production likely comes from a common prototype."

"Our findings also show that humans, despite how complex we are, across the evolutionary lines all the way to flies, which are very simple, still have one fundamental element that's shared," Xu said.

"It's really surprising because sperm production gets pounded by natural selection," said Xu. "It tends to change due to strong selective pressures for sperm-specific genes to evolve. There is extra pressure to be a super male to improve reproductive success. This is the one sex-specific element that didn't change across species. This must be so important that it can't change."

To further support his hypothesis that Boule is widespread across all animals producing sperm and eggs, Xu also examined the genome of one of the most primitive animals, a sea anemone, for the presence of Boule. He looked at its genome because the sperm of the sea anemone is difficult to find and few labs study the animal. When Xu identified Boule in the sea anemone genome, his theory was clinched.

Xu had an interesting shopping list for his search for Boule's presence across the spectrum of evolutionary development. He needed sperm from a sea urchin, a rooster, a fruit fly, a human and a fish. The fish proved to be the toughest.

Xu purchased a rainbow trout at a Chicago fish market, unwrapped it and was dismayed to discover it had been gutted. "I need the testicles!" he exclaimed  to the seafood vendor. Xu decided he'd have to catch his own. He cast a fishing line into a recreational pond stocked with trout and reeled in a rainbow trout.

Discovery of this common gene involved in sperm production could have many practical uses for human health, including male contraception. When Xu's research group knocked out the Boule gene from a mouse, the animal appeared to be healthy but did not produce sperm. "A sperm-specific gene like Boule is an ideal target for a male contraceptive drug," Xu noted.

Boule also has the potential to reduce diseases caused by mosquitoes and parasites such as worms. "We now have one strong candidate to target for controlling their breeding," Xu said.

"Our work suggests that disrupting the function of Boule in animals most likely will disrupt their breeding and put the threatening parasites or germs under control. This could represent a new direction in our future development of pesticides or medicine against infectious parasites or carriers of germs."

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SOURCE: PLoS Genetics, July 15, 2010.